Eggs in the tissue of S. japonicum infected mice persisted in unchanged numbers in the tissues for at least 1 year after chemotherapeutic cure of infections of 8 weeks duration. Worm burdens decreased with time in S. mansoni infected mice between the 8th and 20th week of infection. No dead worms were found in the liver and the decrease in worm burden was caused by death of more heavily infected and shunting of worms from the portal system to the pulmonary arterial circulation.